The present invention relates generally to a fan apparency arrangement. More particularly, the present invention relates to a fan apparency arrangement for an appliance and an appliance incorporating such a fan apparency arrangement.
Appliances such as cooking ranges and wall ovens are widely used. A cooking range typically includes an oven with a front-opening access door, and at least one heating element for heating up the inside of the oven cavity. Wall ovens have a similar configuration. As is known in the art, when energized, the heating element can heat up the inside of the oven cavity to a relatively high temperature. Also as is known in the art, such cooking appliance often has a fan which is used to draw cooling air into the interior of the appliance to cool a structural component of the appliance, such as the front-opening access door, or a heat sensitive component such as an electronic control. If an appliance employs a fan for cooling, some certification institutions, such as Underwriters Laboratories Inc. (UL), require that a fan apparency device (FAD) be employed to determine or detect whether the fan is working properly.
As is known in the art, when a user selects or chooses a heating operation for the oven and turns on the oven, the turning-on also activates the fan. If the fan is working properly, the FAD enables the selected heating operation for the oven to proceed. On the other hand, if the fan is stalled or not working properly, the FAD prevents the selected heating operation for the oven from proceeding.
Various types of FADs are used to determine or detect whether the fan is working properly. The most widely used FADs are thermal switches and sail switches. A thermal switch uses the heat from the oven to heat up a bimetal member of the switch to turn off the switch when the airflow from the fan is not sufficient to cool off the bimetal member. Since the thermal switch usually is not disposed adjacent the intake end or the discharge or exhaust end of the fan, it does not negatively affect the airflow passing through the fan. However, the thermal switch has a relatively slow reaction time. In addition, the thermal switch needs to be installed in an area of the oven where the temperature can rise quickly when the oven is turned on. Moreover, the thermal switch requires extensive testing to prove that it will work as intended in all working conditions of the oven.
A typical sail switch uses the airflow generated by the fan to move a sail to turn on or off the switch. Compared with the thermal switch, the sail switch has a relatively fast reaction time, and requires less testing. However, since the sail is disposed downstream and in the flow-path of the fan, it negatively affects the airflow passing through the fan. Additionally, the sail becomes an undesirable dynamic load for the fan.